Electron beams are now in widespread use in the radiation treatment of cancer because their rapid dose falloff minimizes irradiation of critical healthy tissues beyond the treatment volume. Unfortunately, for treatment planning purposes it is not yet possible to routinely calculate the absorbed dose distribution accurately, particularly in the presence of localized tissue inhomogeneities such as air cavities, bone, and lung. The overall goal of the proposed research is to develop electron dose- calculation algorithms which are sufficiently accurate for the most complicated situations expected to be encountered clinically, yet practical in the sense of being able to be implemented in a computerized treatment planning system (short enough calculation time). The goal of the project is to achieve in these computer algorithms an accuracy of 5%, or preferably 3%, throughout the treatment volume. A Bipartition Model for electron transport has already been developed, and this model will be extended through incorporation of recent multiple- scattering theories describing the forward-directed beam electrons. This will be accomplished through use of the basic laws of physics in conjunction with mathematical simplification of the resulting formulas, to obtain short calculation times while maintaining accuracy. The accuracy of the combined model as it develops will continually be checked through EGS4 Monte Carlo calculations and, later into the project, with experimental dose distributions using a medical electron linear accelerator.